1. Field of the Invention
This invention relates to highly absorbent filaments and webs as well as methods for making them. More specifically, it pertains to improvements having general utility in processes for solvent drying fibrous materials such as the method described in copending and co-assigned U.S. patent application Ser. No. 402,311 to Lassen entitled "Filaments of Chemically Modified Cellulose Fibers, Method of Making Such Filaments and Webs and Products Produced Therefrom" filed Oct. 1, 1973. As described therein, filaments of chemically modified cellulose fibers and webs constructed from such filaments that exhibit, for aqueous systems, high absorbency and wicking properties which can be controlled and varied from slow to very fast are produced by extrusion of chemically modified cellulose fibers and solvent drying. Such filaments and webs are particularly suitable for applications where it is desirable to draw a liquid away from a surface and concentrate it in a particular layer or location. These applications include, by way of example and not limitation, disposable diapers, sanitary napkins, wipes, surgical sponges and the like.
2. Description of the Prior Art
The chemical modification of cellulose to increase its absorbency has been previously described and can be considered in a broad sense to fall into three major classifications in terms of methods:
A. Chemical substitution, etherization, or esterification; PA1 B. Chemical substitution plus cross-linking; and PA1 C. Polymeric grafting.
For example, U.S. Pat. No. 3,670,069 to Mitchell is directed to absorbent fibers formed by extruding solutions such as those prepared from a hydroxyalkyl cellulose. As examples of category "a" above, Bernardin U.S. Pat. Nos. 3,658,790; 3,691,154; and 3,739,782 disclose absorbent fibers and batt-like mats formed from phosphorylated cellulose or its acid form and products incorporating them. An example of category "b" above is U.S. Pat. No. 3,589,364 to Dean et al which discloses absorbent structures including crosslinked fibers of carboxymethylcellulose and products made therefrom. Category "c" above is exemplified by the formation of acrylonitrile grafted cellulose absorbent fibers and products as disclosed in U.S. Pat. Nos. 3,194,727 to Adams et al; 3,455,643 to Gruber et al; 3,065,041 to Soon; and 3,046,078 to Salsbury.
The above-mentioned Lassen patent application describes the formation of absorbent and highly wicking web and filament structures by extrusion and solvent drying of extrudates composed of highly swollen, hydrophilic, chemically modified cellulose fibers such as, phosphorylated pulp fibers or carboxymethylcellulose fibers. Extrusion into a solvent bath results in rapid drying of the fibers forming soft, highly wicking filaments which can be collected to form a web. In web formation various degrees and types of bonding may be obtained, depending, in part, upon the particular conditions of drying.